Sleeper block units are used in so-called slab tracks which are increasingly preferred to so-called ballasted tracks since they allow an increased performance of the track with regard to the attainable speeds and reduced maintenance costs. Such sleeper block units comprise a sleeper block generally made of concrete, a shoe generally made of shaped rubber that receives the sleeper block, and an elastomer pad that is arranged between the bottom of the sleeper block and the bottom of the sleeper shoe. On the upper side of the sleeper block, a fastening system for a rail is arranged. The sleeper shoe is encased in concrete.
In patent DE10196374B4 it is explained that in such sleeper block units the dynamic to static rigidity ratio increases with the vertical movement of the block and therefore the deformation of the elastomer pad under dynamic loads is impeded by an interface between the block and the shoe wall, and that this interface is a phenomenon known as the wedge effect. The cited patent then describes a solution for eliminating the wedge effect without reducing the lateral resistance of the track and for decreasing the dynamic to static rigidity ratio. It is evident that the rigidity and the damping behavior of a sleeper block unit are adversely influenced particularly when solid particles such as sand, dust, dirt, abraded concrete etc. enter between the block and the shoe. Therefore, measures aiming to seal the space between the block and the shoe against the exterior have already been suggested.
The references EP1017906B1 and DE4335516A1 both show a sleeper block having a partly surrounding sleeper shoe where a resilient sealing lip lying against the substantially vertically oriented outer wall of the sleeper block is arranged at the upper edge of the sleeper shoe. These arrangements suffer from the disadvantage that during vertical movements of the sleeper block, the sealing lip rubs against the outer wall of the sleeper block and is therefore subject to wear so that the sealing effect decreases over time. The reference EP0915202A1 describes a sleeper block and sleeper shoe assembly where the latter has a surrounding sealing arrangement at its upper edge that sealingly engages in a dedicated surrounding groove in the sleeper block. This groove complicates the manufacture of the sleeper block.
In the reference DE4335516A1 it is also suggested to additionally seal the junction between the sleeper block and the shoe by means of an adhesive strip. On one hand, the attachment of the adhesive strips involves considerable labor during the construction of a slab track, and on the other hand, it is to be expected that the sealing effect of the adhesive strips will decrease over time.
The reference EP0557870B1 describes a solution where a surrounding sealing frame of an elastic material is provided in the area of the upper edges of the sleeper block side walls, whose lower edge section overlaps the upper edge of the sleeper shoe side walls externally and which is sealingly connected thereto, and whose upper edge section is sealingly connected to the lateral surfaces of the sleeper block. More specifically, this upper edge section of the sealing frame may be encased in the sleeper block, and the lower edge section is preferably connected to the sleeper shoe by bonding or welding. In addition, as shown in FIG. 2 of the document, the junction area of the sealing frame is covered by the surrounding concrete. Although this arrangement ensures the required tightness, it entails considerable difficulties when a sleeper block needs to be replaced. Lifting out a sleeper block requires a substantial force whereby the sealing frame will generally be destroyed so that fragments of the sealing frame will inevitably be left on the sleeper shoe and make it even more difficult to tightly attach a new sealing frame to the sleeper shoe. Correspondingly, the insertion of a new sleeper block will be problematic, and a reliable seal of the new sleeper block can only be achieved by partly removing the surrounding concrete and re-encasing the sleeper shoe when the sealing frame of the new sleeper block has been bonded or welded, respectively.